The stylus is the first link in
the reproducing chain of the phonograph record and, unfortunately,
often the most neglected. Giving more attention to the state of your
stylus will pay off for you in better listening, but will also allow
you to protect your most precious investment - your favorite records.
If you are typical, you tend to spend much more on your records than
on hardware or your equipment. And some records are irreplaceable.

The task of your stylus is
formidable. For every hour of music played your stylus travels more
than one mile. Great efforts are made to minimize the wear and tear
on your extremely delicate stylus during its long journey along the
moving groove wall. The stylus is highly polished, and the groove
walls are burnished by the recording stylus to reduce the roughness
to less than 3 millionths of an inch. With all this effort there
still remains a small amount of unavoidable friction in the
interaction between the hardest substance known, the diamond stylus,
and the necessarily compliant and rubbery vinyl of the disc. Happily,
the vinyl under friction will temporarily yield and then spring back
rather than wear away.

The diamond, as hard and wear
resistant as it is, will wear even though its wear rate is only a
molecule or two per foot of groove travel. As the stylus wears under
constant friction of tracing the record, it begins to assume a
deformed shape. This new slowly evolving stylus shape adversely
affects the performance of your hi fi system and, if allowed to
continue beyond a certain point, will damage the groove walls of your records.

So the important and practical
question becomes, "When should I replace my phonograph cartridge
stylus?" To understand the answers to this question, it will
help if you understand the function of the playback stylus in the
reproduction chain, and how it affects the quality of the sound and
music from your high fidelity system".

Stylus Function

First, let's examine the record
with a microscope. Microscopic inspection of the record will show a
continuously undulating "V" groove molded into the surface.
The undulations of the groove are a precise mechanical replica of the
acoustic waves generated by the original musical performance, as
recorded onto a master tape from which most records are made. The
disc recording art has reached such a high state of development that
the information on the master tape can be transferred to the disc
with virtually no change or degradation.

The stylus has the critical task
of tracing these superfine undulations. The stylus must change
direction up to 4,000 times a second in one inch of passing groove
wall in the inner grooves of the average disc, and transmit these
groove undulations to the electronic system of the cartridge. The
stylus, married to the cartridge, converts the mechanical motions of
the disc into electrical voltages. Together the stylus and the
cartridge act as a transducer - a translator of the mechanical to
electrical. Your speaker system does just the reverse. The speaker
translates the electrical into the mechanical motions that move the
air and make sound.

Picture your playback stylus as a
ball sliding along a groove modulation as shown in Figure 1.

Use of the ball analogy (insofar
as it demonstrates the tracing function) to represent the stylus
holds true for spherical, elliptical, and for the new CD-4 styli such
as the Quadra-Point and Shibata. To simplify the illustration only
one groove wall is shown. Actually, the groove moves past the stylus,
but in flat, static illustrations, it's easier to show the groove as
stationary and the stylus sliding along the groove. As the record
moves past the relatively stationary stylus, the stylus executes a
motion that is the precise duplicate of the groove undulation, moving
in two directions at once, both vertically and horizontally, up and
down, with the constant varying depths of the record's groove and
from side to side. When the stylus does its job well, the groove is
precisely traced and the stored information on the groove is retrieved.

Worn stylus

A worn stylus will not retrieve
this stored information properly. In Figure 1 the stylus is
represented by a perfect sphere. As the surface of the stylus is
abraded away its shape changes as in Figure 2.

Figure 2.

Stylus shape changes with wear

In this illustration we show the
wear on both sides of the stylus since in actual playback the stylus
is in continuous contact with both sides of the groove. As wear
starts a slight flat appears on both sides of the stylus. As wear
continues these flats become larger. In extreme cases of wear as
shown in Figure 2D, the original ball shape has worn into a shape
represent- ing a screwdriver tip. If we play the same groove
undulation shown in Figure 1 with a moderately worn stylus, we can
hear the effect on our fidelity play-back system. As the worn stylus
traces the groove, as in Figure 3,

Figure 3.

Stylus motion a distorted version of groove undulation with worn stylus

the path of the stylus no longer
represents a replica of the groove undulations. The effect is the
same as playing the record groove with a considerably larger stylus
than was intended. When the path of the stylus differs from the shape
of the groove undulations, increased distortion is the result. For
good reason, engineers call this tracing distortion, for what the
worn stylus now does is feed a distorted version of the groove
undulation to the electrical system of the cartridge. As the stylus
wear increases, the amount of distortion increases until the
screwdriver shape is reached. At this stage further problems are introduced.

Some years ago when I, was
director of disc research at CBS Laboratories, we were studying the
effects of worn playback styli on playback distortion. One of
Columbia Records quality con- trol procedures in their pressing
plants was to actually play one record out of each spindle of records
to make certain that the stamper in use at the time had not developed
defects. Quite a few worn styli were generated by quality control
testers, and we got a hold of a handful of the styli. To my surprise,
I found out that flats worn on the styli were barely perceptible,
even with the very sophisticated microscopes we had at our disposal.

I was very skeptical when I found
out that the testers reported that, "The cartridges didn't sound
good anymore," and that there was no mandatory visual inspection
of the rejected styli. I could not have been more wrong.

When I visited the plant and
spent some time with the quality control testers, I found out some
interesting things. It's important to realize that when it's
somebody's job to listen to records all day long and pick out those
records that don't sound right, these listeners develop an extreme
sensitivity to deterioration in sound quality. One of the testers
gave me a convincing demonstration with a stylus I had brought with
me. The stylus was typical of the styli discarded because of wear.
Under the microscope two extremely small flats could be seen. Without
her looking, I interchanged a good stylus with the slightly worn one,
back and forth a number of times. Each time, by the presence or lack
of distortion, the tester could instantly tell me which stylus was
installed. By the end of the session I could readily tell the
difference myself.

So far we have mentioned how
stylus wear affects tracing function. In the more extreme cases of
wear, when the stylus begins to look like a screwdriver tip, there is
not only playback distortion, but damage to our precious records. In
Figure 4

Figure 4.

Severely worn stylus can cause groove damage.

we show a "screwdriver
tip" stylus sliding along the groove wail. You can see that this
new shape of the stylus will not slide harmlessly along the groove
wall and permanently damage the record. Styli worn to this extent are
not so rare as you might think.

When To Replace Your Stylus

So the 'when' answer to the
question, "When and why shall I replace my stylus?" is - as
soon as you hear an increase in distortion.

A word of caution: Not every case
of distortion can be attributed to a worn stylus. Some judgment and a
little intelligent experimentation may be necessary to determine
where the distortion originates. Usually the first subtle indications
of stylus wear can be detected in your own listening room when you
hear increasing distortion, especially on sibilance in voices. If you
want to know whether your stylus is approaching conditions of extreme
"wear, take your stylus to one of the many hi fi retail shops
that have a stylus inspection service.

To the oft asked question,
"Is there a set number of playing hours be- fore a stylus should
be replaced?" my answer is no. Tracking force and other playing
conditions vary. The slightest variation in diamond quality and
groove wall surfaces make it very difficult to predict the number of
playing hours of stylus life.

My best advice - when in doubt,
replace the stylus. Your stylus investment is relatively modest when
you consider what you've spent on the rest of your equipment and your
sometimes irreplaceable records. The stylus is not the place to
scrimp. A new stylus can bring your record playback system to peak performance.

The motto: Trust your ears for
the most practical test for determining if your stylus is performing properly.

Written by Arnold Schwartz 1972,
former President of the Micro-Acoustics Corporation.

Published as an enclosure to the
Micro-Acoustics cartridges for common information.